Leakage current protection switch with excess current release



Fel). 11, 1969 s. BIEDERMANN 3,427,505

LEAKAGE CURRENT PROTECTION SWITCH WITH EXCESS CURRENT RELEASE Flleu' Jan. 17. 1967 Sheet of 2 R s T FIG. I.

TRANSFORMER TRANSFORMERS INVENTOR SIEGFRIED BIEDERMANN BY MW ATTORNEY.

Feb. 11; 1969 s, BiEDERMANN 3,427,505

LEAKAGE CURRENT PROTECTION SWITCH WITH EXCESS CURRENT RELEASE Filed Jan. 17. 1967 Sheet 2 oi 2 QOI l 2 3 4 5 6 7 8 9 |OXJN INVENTOR SIEGFRIED BIEDERMANN ATTORNEY.

United States Patent LEAKAGE CURRENT PROTECTION SWITCH WITH EXCESS CURRENT RELEASE Siegfried Biedermann, Schellenberg, Liechtenstein, as-

signor to Uninorm Anstalt, Vanduz, Liechtenstein,

a corporation of Liechtenstein Filed Jan. 17, 1967, Ser. No. 609,850

Claims priority, application A6ustria, Jan. 25, 1966,

A 684/6 US. Cl. 317-18 Int. Cl. H02h 1/02 8 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a leakage current protection switch with excess current release.

Leakage current protection switches for electric relay systems have hitherto been designed mainly as load switches exercising a protective function only against inadmissible earth leakage currents.

In practice, however, there is a great need for switches of this kind which, in addition, provide protection against excess current. On the one hand, this makes possible a reduction in the dimensions of the protective switch on its nominal current (and not the small test current of a connected fuse of the same nominal current) and on the other hand, it increases the total protective quality of the switch as it frees the overload protection from the inherent inaccuracy of fuses and their operating problems.

Ideally, the protective switch should provide protection against electric shock by providing protection against leakage currents and should also provide protection against overloading and short circuits. As yet, no fully satisfactory solution to the problem of providing this combined protection has been found because combinations of summation current transformers, bimetal releases and short circuit release coils are economically too costly.

A number of earlier patent specifications do refer to simpler solutions than those just mentioned, but these solutions are far from ideal. For example, in Austrian patent specification No. 220,695 an arrangement is described which by the use of a highly sensitive leakage current protection magnetic release at least one addi tional short circuit protection, but no overload protection is attained.

Other solutions are based on an additional rotating wedge pawl release for the switch lock operated by a bimetal deflection which is brought about by the temperature within the narrow switch casing. But here a built-in short circuit protection is dispensed with. A further solution ('Austrian patent specification No. 235,936) provides in the magnet release sof-t magnetic material with low Curie-Point whereby the release is formed as a stop magnet. Here, of course, the ambient tempenature affects the characteristics of the leakage current protection which means that at low temperatures the size of the release current increases. From the point of view of providing a reliable protection against electric shock hazards, this is impermissible. Finally, in German Auslegeschrift No. 1,188,706, there is described an arrangement providing excess current and a short circuit release in a leakage current protection switch in which a summation current transformer is used and measuring members (short circuit magnets, thermal releases) responding to overcurrent or short circuit associated with the individual mains phases close upon release of a circuit which leads via a special working winding (tertiary winding) of the summation current transformer.

It is one object of the present invention to provide a leakage current protection switch with excess current release, which switch comprises a summation current transformer connected in circuit with a magnetic release to provide leakage current protection and to provide excess current protection, a negative temperature coefficient resistance arranged in heat-conducting relationship with the summation current transformer in circuit with a second magnetic release fed via transformers in the phase leads of the protected circuit with a voltage dependent upon the currents flowing in the phase leads.

With this and other objects in view, which will become apparent in the following detailed description, the present invention will be clearly understood in connection with the accompanying drawings, in which:

FIGURE 1 is a basic circuit diagram of a switch according to the present invention;

FIG. 2 discloses details of the basic circuit diagram illustrated in FIG. 1;

FIG. 3 shows an advantageous construction of the summation current transformer; and

FIG. 4 shows a release curve.

Referring now to the drawings, and in particular to FIG. 1, a leakage current protection switch is disclosed, which works according to one of the known residual magnetic release principles, whereby a release magnet 7 is disposed across two galvanically separated release windings W W One of the two release windings, namely the winding W is excited by the secondary winding of a summation current transformer 1 in conventional manner. The other of the release windings, namely the winding W is connected in series with a negative temperature coefficient resistance 2 to form a circuit completely separated electrically from the winding W thus preventing any undue electrical influence on the winding W A resistance 2 is disposed inside the summation current transformer 1 which can be regarded simply as a heat bed, which arrangement constitutes one of the features of the present invention, the temperature of which heat bed represents a measure of the currents in the mains conductors. This circuit, including the resistance 2 and the second release winding W is fed by a voltage derived from the currents in the phase conductors via a current transformer (or several current transformers) 3-.

Referring now again to the drawings, and in particular to FIG. 2, the voltage fed to release winding W and resistance 2 and which represents a measurement of the phase currents, is advantageously derived in such a way that the three current transformers 3 in the other leads are connected in a star delta arrangement and supply a direct voltage via a rotating current half-wave rectifier comprising three diodes 4 and a smoothing condenser 5. The direct voltage increases with increase of the phase current irrespective of whether in one, in two, or all three outside leads and conversely decreases with decrease of the phase current. The smoothing condenser 5 can be selected sufiiciently large, so that it is charged irrespective of the number of current conducting outer leads always corresponding to the peak value of the alternating current and thus supplies a current measurement independent of the number of loaded or overloaded conductors. If the leakage current release is constructed 3 as a stop magnet or holding magnet (for example, as described in Austrain patent specification No. 244,427) attention must be paid to the correct polarity of the release winding W In accordance with the basic concept of the present invention, in the present release switch, the negative temperature coefiicient resistannce 2, decisive for providing the increased current in the release winding W to effect the excess current release, is located in the geometric center of the summation current transformer 1.

This arrangement is particularly simplified if, as FIG. 3 shows, the summation current transformer 1 is a ring core transformer with primary winding number equal to one, whereby the ring core 8 closely surrounds the mains leads 9 which are threaded through it.

The size of the secondary voltage of the current transformers 3 like all further elements of the circuit of the release winding W must now be so chosen, that with nominal current and small overcurrents 10%) the excitation due to the release winding W is not yet sufficient for the release. With higher overcurrents the direct current flowing through the release winding W increases due to the higher transformer secondary voltage. This approximate linear increase does not suffice alone for the release. On the contrary, resistance of the negative temperature coefficient resistance 2 in the heat center of the summation current transformer must be reduced corresponding to its increase in temperature, so that there results an inverse release time-release current characteristic to effect the release. With overcurrents which are multiples of the nominal current, in particular with short circu-it currents, the sole (and immediate) increase of the direct voltage on the smoothing condenser 5 suflices in order to lead to a momentary release.

Referring now again to the drawing, and in particular to FIG. 4, the whole release curve of the present switch is shown and illustrates the dependence of the release time t on the nominal current I An advantageous development of the switch described consists in replacing the three individual phase current transformers 3 by a single multi-armed transformer.

A suitable development of the switch described in order to attain independence from greatly fluctuating ambient temperatures consists in that in the circuit of the second excess current excited release winding W compensating switch elements 6 of the same or similar temperature characteristic as the resistance 2 are arranged in the circuit, as shown in broken lines in FIG. 1, and are located so that their resistance values are determined primarily by the ambient temperature.

The leakage current protection switch described is suitable as a motor protection switch.

While I have disclosed several embodiments of the present invention, it is to be understood that these embodiments are given by example only and not in a limiting sense, the scope of the present invention being determined by the objects and the claims.

I claim:

1. A leakage current protection switch with excess current release for a protected circuit, the switch comprising a first magnetic release,

a summation current transformer connected in circuit with said magnetic release, to provide leakage current protection and to provide excess current protection,

a second magnetic release,

a negative temperature coefficient resistance arranged in heat-conducting relationship with said summation also current transformer in circuit with said second magnetic release,

transformers in phase leads of the protected circuit, and

said second magnetic release being fed via said transformers with a voltage dependent upon currents flowing in said phase leads.

2. The switch, as set forth in claim 1, wherein said negative temperature coefiicient resistance is located at the geometrical center of said summation current transformer.

3. The switch, as set forth in claim 2, wherein said summation current transformer is formed as a ring core transformer having a primary winding number equal to one, and whereby said ring core closely surrounds the main leads which are threaded through it.

4. The switch, as set forth in claim 1, wherein said second magnetic release comprises a holding magnet and a release winding which is fed via said transformers.

5. The switch, as set forth in claim 4, wherein the size of the secondary voltages of said transformers in said phase leads and the resistance values of said negative temperature coefficient resistance and the characteristics of said release winding are so chosen that with no more than slightly higher than nominal current in said phase leads no release occurs, with impermissible excess current a correspondingly progressive decrease of the value of said negative temperature coeflicient resistance occurs with eventual release, and with short circuit immediate release occurs.

6. The switch, as set forth in claim 4, which includes at least one compensating resistance, having at least similar temperature characteristics as said negative temperature coefiicient resistance, is disposed in the circuit of said release winding and so located that its resistance is determined primarily by the ambient temperature.

7. The switch, as set forth in claim 4, wherein said release winding is excited by a direct current obtained from said phase leads via three current transformers having three secondary windings, and

three phase rectifiers in delta star arrangement and a smoothing condenser arranged in parallel with said negative temperature coeflicient resistance switching in series and said release winding and between the star points of said three secondary windings of said current transformers and said three phase rectifiers.

8. The switch, as set forth in claim 7, wherein said three current transformers are assembled by means of multi-armed cores to form a single transformer.

References Cited UNITED STATES PATENTS 11/1964 Gagniere et al 317-18 10/1965 -M0ser et al. 317-18 FOREIGN PATENTS 5/ 1933 Great Britain. 7/ 1952 Great Britain.

US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,427 505 February 11, 1969 Siegfried Biedermann appears in the above identified It is certified that error ent are hereby corrected as patent and that said Letters Pet Show below:

ading to the printed specification, line 5, "-Vanduz" should read In the he Vaduz Signed and sealed this 24th day of March 1970.

Attest:

WILLIAM E. SCHUYLEB, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

